A rack-mounted server is a server whose appearance is designed according to a uniform standard. The objective of designing the rack-mounted server is mainly to reduce space occupied by the server as much as possible. Network devices employing the rack-mounted server include, for example, a switch, a router, and a hardware firewall, etc. The rack-mounted server has a width of 19 inches and a height in a unit of U (1U=1.75 inches=44.45 mm). Usually, the servers have several standards: 1U, 2U, 3U, 4U, 5U, and 7U, etc.
One kind of rack-mounted servers includes a plurality of chassis each having an opening at a front end. A back-plane is disposed at a rear part of each chassis. A drive assembly can be plugged into a corresponding back-plane along a horizontal direction through the front-end opening on the chassis. In such a server, each drive assembly includes a drive and a corresponding carrier device. The drive carrier device provides an interface component plugged into the back-plane along the horizontal direction. However, for such a rack-mounted server, because only one row of drive assemblies can be plugged into each chassis, the chives in the server have a relatively low density.
Another kind of rack-mounted server includes a plurality of chassis each having an opening at the top. There is provided a plurality of back-planes spaced from each other in each chassis. After a drive assembly is placed into a space between neighboring back-planes, it may be plugged into the corresponding back-plane along a horizontal direction. In such a server, each drive assembly also includes a drive and a corresponding carrier device. The drive carrier device also provides an interface component plugged into the back-planes along the horizontal direction. Such a rack-mounted server allows arrangement of a plurality of rows of drives in a single chassis, which increases drive density to a certain extent. However, for such a rack-mounted server, a certain space (e.g., 2 cm) needs to be reserved between neighboring back-planes so as to allow plugging the drive assembly along the horizontal direction, which thus reduces space utilization of the chassis.